Regulated power supply



w. R. AYRE'S ETAL REGULATED POWER SUPPLY Sept. 30, 1952 Filed Aug. 30, 1949 "M VOW v W sm. k

a J 5 5. mm m mw v m w H Patented Sept. 30, 1952 UNIT-ED s'm'rs's [PATENT OFFICE 'REGULATED rowan SUPPLY WilliamR. Ayres, Oaklyn, and Harry J. 'Woll, AuduboxnN. 'J., assignorsto Radio Corporation of America, a corporation of Delaware Application August 30, 1949, Serial No. 113,226

5 Claims.

This invention relates generally to voltage regulating devices, and-more particularly toan improvement in electronically regulated DL-C. voltage power supplies.

Electronically regulated power supplies are genera-11y used where a pure and steady D.-C. voltage supply must be obtained from an available A.-C. power source. In the electronically regulated power supplies presently known to the art, a control tube samples the output voltage of a power supply and, in accordance with this voltage sample, controls a variable resistance tube through which the load current must pass. The voltage sample is usually obtained from a tapped bleeder resistor which is placed across the power supply output.

It has beenfound, however, that'the D.-C. output from these prior art power supplies still contains power supply ripple and hum voltages usually caused by pickup in the w'iringand or by the A.- C. voltages used to "heat the tube filaments. To correct this condition, a condenser is used to by-"pass the undesired A.-C. voltages from the output of the power supply directly to the grid of the control tube. The corrective action thus introduced is still insufficient, since A.-C. noise consisting of ripple and hum voltages is still pickedup by the wiring coupled to the grid of the controltube and is thereby introduced into the system.

Asa further means foreliminating these unwanted A.-C. noise voltages, it has been proposed to place a filter condenser across the output of the power supply in addition to the above mentioned by-pass condenser. However, since an electronically regulated power supply is a substantially constant voltage source, its output impedance is very low, generally on the order of 5 to 150 ohms. This is a very desirable characteristic from the standpoint ofgood voltage regulation. If afilter condenser is to be effective, however, it mustbe supplied from a source preferably having a high or substantial impedance. Otherwise, the filter time constant obtainable when using the usual or reasonable values of filter condensers is relatively short, and extremely poor filtering action results.

As a compromise measure, in order to obtain reasonably good filter action with the normally obtainable filter condenser values, and in order to keep the output impedance of the powersupply reasonably low, it has been proposed to raise the source impedance value by means of a resistor insorted in series in the load current carrying line between the variable resistance tube and the point of connection of the bleeder resistor used for output voltage sampling. The value of resistor' selected was on'the order ofa few hundred ohms. The by-pass condenser was connected from the control tubegridto the side of the resistor nearest to the "variable resistance tube. This-was'done in order that the-A.-'C. noise voltagesamp'lebe as large aslieretofore and'in order not to introduce, "as additional modulation, any stray voltages that mightbe picked up by the filter resistorand its-leads.

These-measures proved'effective to substantially eliminate the 'A- C. noise voltages whilethe regulatingaction of the powersupplyis not perailect-ed witha substantially constant load. However, 7 is is-"found that, with changes in load, transient voltage disturbances occur. The e'fiect and extent of these transient voltage disturbances varies with theamount of load change. It is 'also found that these transient voltage disturbances a're attritutable to the network components added to the power supply, as indicated above, for the purpose of eliminating the A.-C. noise voltages from the power supply output volt- It is, therefore an'object of our invention to provide an improved electronic power supply ceptibly wherein transient voltage disturbances due tov changes in loadare substantially eliminated from the output voltage. v I I i It is a further object of our invention to provide an improved electronic power supply wherein both transient voltage disturbances due to load changes and A C. noise voltages are substantially eliminated from the output voltage of the power supply.

It is still "a further "object of our invention to provide an improved electronic power supply having better voltage regulatory action than heretofore.

These and other objects are achieved in accordance with this invention by using a high pass filter for feeding A.-C. noise voltages back to the control tube grid in place of the b'y-pass'condenser. Sincethe point of A.-Cv noise voltage feed-back is'also the point where the greatest transient voltage occurs on changes of load, the transient voltage, which is a low frequency disturbance, is not by-passed to the control tube grid, while the A.-C. noise voltages which are on the order of power line frequencies are bypassed to the control tube grid substantially undiminished.

The novel features of our invention, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description of several illustrative embodiments thereof, when read in connection with the accompanying drawings in which like reference characters are applied to parts having similar functions and wherein:

Figure l is a schematic diagram of a prior art electronic power supply with A.C. noise voltage filtering, which is necessary for an understanding of our invention, and

Figures 2 and 3 are schematic diagrams of two preferred embodiments of our invention and their connections to the power supply of Figure 1.

Referring to Figure 1 of the drawings, there is shown a power transformer l having a primary winding I2, to which the A.-C. power is applied, and secondary windings l4, I6, I 8 and 22. Secondary winding [4 is the voltage step-up portion of the transformer 10 in which a high voltage is induced in well known manner. The remaining secondary windings l6, l8, and are used for heating, in well known fashion, the tube filaments used in this apparatus. v

A rectifier tube 22 is provided having a cathode 24, which is heated by means of the secondary winding [6, and a pair of anodes 26, 28 which are connected to the ends of the secondary winding [4. A center tap on the secondary winding 14 is connected to ground or to one side of a filter network associated with the rectifier tube.

The filternetwork shown is the pi-type and comprises a pair of condensers 30, 32 connected from opposite sides of a filter choke 34 to ground. One end of the filter choke 34 is connected to the cathode 22, as is conventional, and the other end is connected to the plate of one or more variable resistance tubes 36, 38. A voltage divider resistor is also connected between the output end of the filter section and ground. A regulator tube 42 is connected to one portion of the voltage divider resistor 46. The cathode of a control tube 44 is connected to the lower portion of the voltage divider resistor 40. The purpose of the connections shown is to insure that the cathode potential on control tube 44 is constant regardless of the power supply fluctuations. This is obtained by having the voltage divider resistor 48 draw a fairly high current. Any fiuctuations in this current are compensated for by operation of the regulator tube 42 in a manner well known in the art.

A voltage divider resistor 46, which is across the filter network output, is tapped to supply screen voltage to the control tube 44. A resistor 48 couples the plate of the control tube 44 to the output from the filter section and serves as the plate load resistor. A condenser 50 is connected from the screen of control tube 44 to ground and is the conventional screen by-pass condenser. Another condenser 52, which is connected from a tapped portion of the resistor 48 to ground, is the plate decoupling condenser. A condenser 54 connected between the cathode of control tube 44 and ground serves as the cathode by-pass condenser. The plate of the control tu e 44 is coupled to the grids of the variable resistance tubes 36, 38 through oscillation suppressing resistors 56, 58. The cathodes of the variable resistance tubes 36, 38 each have current equalizing resistors 6!], 62. These current equalizingv resistors 60, 62 connect from the cathodes of variable resistance tubes 36, 38 to a filter resistor 64. The other end of the filter resistor 64 is connected to the load 66. A filter condenser 68 is connected age therefore increases.

to the grid of the control tube.

' In the operation of the power supply, the potential at the plate of the control tube 44 is substantially that of the control grids of varia le resistor tubes 36, 38 and therefore the control tube plate potential determines the amount of current which flows through the variable resistor tubes 36, 38. The control tube plate potential, however, is determined substantially by the control tube grid voltage since the control tube cathode voltage is maintained substantially constant. The output voltage at which the power supply operates is, therefore, substantially determined by the voltage which is tapped from the variable portion of the bleeder resistor 70. Once the output voltage is thus selected, any increase in output voltage results in an increased voltage at the grid of the control tube 44, causing a lower potential at the control tube plate and also at the variable resistor tube grids, thereby reducing the amount of current they can pass. The output voltage is thus maintained substantially constant. A decreas in the output voltage results in a decreased voltage being applied to the grid of the control tube 44. Its plate volt- This results in an increase in voltage on the grids of the variable resistance tubes 36, 38 and they therefore pass more current, thus maintaining the voltage constant. It is thus seen how, by sampling a portion of the output voltage which is across the bleeder resistor 10, voltage regulation may be obtained.

As previously discussed herein, hum and ripple voltages comprisin unwanted A. C. noise voltages are substantially eliminated by being fed to the control tube grid by means of the by-pass condenser 14 and by the action of the R.-C. filter section comprising the filter resistor 64 and the filter condenser 68. Point Z on Figure 1, at the junction of the resistors 62 and 64, denotes an end of resistor 64 from which noise voltages are by-passed and which is coupled to the oathodes of the variable resistance tubes 36, 38. Point Y, at the other end of the resistor 64, denotes an end of the filter resistor 64 to which the bleeder resistor 10 is connected and at which a desired output voltage from the power supply exists. Point W, at the movable end of the resistor 12, represents the point on the bleeder resistor from which the voltage sample for D. C. output voltage variations are obtained. Point V, at the fixed end of the resistor 72, represents the point of connection to the grid of the control tube 44.

The filter resistor 64 has a resistance value usually on the order of 300 ohms. Therefore, when load current is drawn through the resistor 64, point Z will be several volts higher than point Y, depending, of course, upon the value of the load current. Under a typical operating condition, an average load curent of mils causes this potential diiference to be 45 volts. If the load is thrown oiT, or substantially reduced, since the current drawn by bleeder resistor 10 is usually so low as to be negligible, the current through the resistor 64 drops to a small value.

Because of 'the :slow transient "response :of the power supply, the voltage atxpoint Z v;is:.maintained .eiatfthe same level, .:so that; the voltage at point Yrises substantially '45fV01llS'T/0 equal the voltage at point ZZ. aundesirable large stransient voltage rise thu nccurs inth'e Loutputvoltage which, in time, is subsequently eliminated by the regulatingaction of the power supply.

If, by some means, it is attempted to hold the point Y at a constant voltage level when the load current is changed or the load is thrown off, the voltageat point Z will dropquickly through substantially 45 volts with the drop inload current in order to equal the voltage at :point Y. This voltage drop constitutes a transient voltage havm a loworder of frequency but.neverthelessit will be'substantially applied to the grid-.of :the control tube 44 through the by-pass condenser I4 and will cause a correspondingly large transient rise in the voltage output of the power supply. The effect of the transient voltage, therefore, is. to cause the control voltage point to be shifted from the point Y, where a desired voltage level exists, to the point Z, where an undesired transient drop occurs. Of course, in going from av no load to a load condition, all the above described effects occur in reverse. It is to be understood that the magnitude of the transient voltage disturbance caused, with given network components, varies with the amount of load current change. The above diffioulties in obtaining proper voltage regulation are substantially eliminated in our invention.

Figure 2 of the drawings representsa schematic of one embodiment of our invention. From the point Z to the point V are connected two condensers l6, 18 in series, and from their junction point to ground is connected a resistor 80. These series condensers 1 6, I8 and shunt resistor 80 form a high pass filter network which transmits A.-C. signals at power line frequencies but attenuates signals at lower frequencies. Since any transient voltages developed at the point Z due to load changes are at lower frequencies than power line frequencies, these transient voltages will be considerably attenuated by the high pass filter and the transient voltage disturbance will be substantially eliminated from the grid of the control tube 44. Since the A.-C noise voltages are still fed to the grid of control tube 44, the output of the power supply will be substantially as free from these noise voltages as heretofore.

A schematic of another preferred embodiment of our invention may be seen on reference to Figure 3 wherein the series capacitive arms 16, 18 of the high pass filter are connected between the points Z and V as before but the shunt resistive arm 80 is connected between the junction point of the series capacitive arms and the point Y which is a point of relatively low A.-C. potential. Any low frequency transient voltage which occurs at the point Z, as a result of a load change, is not transmitted to the point V because of the attenuation by the high pass filter. A.-C.noise voltages are transmitted to the point V through the high pass filter. Since the point Y is not entirely isolated from the system, at the time of a change in load, a minor transient voltage fluctuation occurs at this output voltage point whichrequires correction. This transient voltage is passed through the resistor 80 and the condenser 18 to the point V, and the proper corrective action then occurs. For slow or substantially D.-C. changes in the output voltage of the power supply, the output voltage sample taken atithe point W1 from the :bleeder resistor lll is ample to effectxcorrectiveaction.

We h'ave' obtained excellent 1 transient voltage elimination (when thezreactancevalue'of the condenser .16 and -theresistanceivalue of the resistor are-made substantiallyequaliat powerline frequencies and substantially :greater :than .xthat .sof the resistor 64. Some :typical values used for'the high pass filter, when themesistor 64sis 300 TOhmS and the condenser 53 :is microfarads, :are 0.1 microfarad for 'the condensers 15 and 31.8 and 22;000-:'ohmsfor the resistor .80. A'value of 1.0 megohm isselected forthe'resistance l2.

We have shown herein1an electronic :powerisupply- -wherein the "control -tube gr-id is effectively connected to three points in :order to iobtain a proper voltage sample for voltage. regulation. The first is the point W where asproper voltage sample is obtained to correct for slow or substantially D.-C. changes in output voltage levels; the second is the point Z where a proper voltage sample is obtained to correct for A.-C. noise voltages; and the third is the point Y where a proper voltage sample is obtained to correct for low frequency transient voltage disturbances in the output voltage level.

. From the foregoing description, it will be readily apparent that we have provided an improved electronically regulated power supply. Although two embodiments of our invention have been shown and described, it should be apparent that many changes may be made in the particular embodiments herein disclosed, and that many other embodiments are possible, all within the spirit and scope of our invention. Therefore, we desire that the foregoing description shall be taken as illustrative and not as limiting,

What is claimed is:

1. The combination of an electronically regulated power supply and a high pass filter, said power supply including a point of substantially low alternating current potential, acontrol tube, said control tube having acontrol grid upon which voltage samples are impressed to obtain regulation of said power supply output voltage, and an output filter section comprising a series resistor having a first and a second end, and a shunt condenser, said shunt condenser being connected to said second end of said series resistor, and said high pass filter comprising series capacitive arms and a shunt resistive arm, said series capacitive arms being connected between said first end of said series resistor and said control tube grid, said shunt resistive arm being connected to said point of substantially low alternating current potential in said power supply.

2. The combination as recited in claim 1 wherein said point of relatively low alternating current potential is at a point of ground potential in said power supply.

3. The combination as recited in claim 1 wherein said point of relatively low alternating current potential is at the junction of said second end of said series resistor and said shunt condenser.

4. The combination of an electronically regulated power supply and a high pass filter, said power supply having a control tube and at least one variable resistance tube through which the load current fiows, said control tube being coupled to said variable resistance tube to regulate said load current flow through said tube, said control tube having a grid to which voltage samples are applied to obtain regulation of said power supply output voltage, said power supply having an output filter section comprising a first resistor connected in series with said variable resistance tube and having a. first end coupled to the cathode of said variable resistance tube, and a filter condenser connected to a second end of said first resistor and across said power supply output, and said high pass filter comprising a first condenser and a second condenser connected in series, said series connected condensers being connected between said first resistor first end and said control tube grid, and a shunt resistor connected between the junction of said first and second condenser and said first resistor second end whereby alternating current noise voltages and transient voltages caused by load changes are substantially eliminated from said power supply output voltage.

WILLIAM R. AYRES. HARRY J. WOLL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,037,267 Rechnitzer Apr. 14, 1936 2,456,638 Kenyon Dec. 21, 1948 

